Embodiments of the present disclosure generally relate to fuel vapor supply systems for supplying fuel vapor stored in a canister to an internal combustion engine via an intake and/or purge passage.
Conventionally, as generally referred to and/or known in the art, a vehicle such as an automobile may be powered by an internal combustion engine that consumes fuel to provide power to, for example, a drivetrain of the automobile to propel the automobile as desired (i.e., forward). Such internal combustion engines may be configured to be in fluid communication with one or more canisters configured to store and/or adsorb fuel vapor supplied from a fuel tank to the engine. Specifically, lines and/or passages connecting the fuel tank, canister and/or engine may be open and shut by control valves with, for example, a “purge control” setting and/or mode. Further, the purge control setting may be associated with a predetermined condition such that if the predetermined condition is met during operation of the internal combustion engine, the purge control may be triggered. In detail, purge control may involve the introduction of atmospheric air into the canister. Fuel vapor accumulated and/or stored in the canister may be supplied to the internal combustion engine via an intake pipe to be combusted. Thus, by performing the purge control, the fuel vapor stored in the canister may be combusted without, for example, being first discharged to the atmosphere. Accordingly, as described herein, an internal combustion engine configured with a purge control setting may be used to minimize environmental emissions by regulating discharge of fuel vapor stored in the canister to the surrounding atmosphere.
However, a quantity of fuel supplied to the engine may proportionately increase in accordance with the quantity of fuel supplied from the canister, rather than the quantity of fuel injected into the engine by injectors. For example, should the internal combustion engine, as described above, use a three-way catalyst to purify exhaust gas, a theoretical air fuel ration of λ=1.0 may be selected to achieve a desirable exhaust gas purification efficiency. Thus, fuel delivery from the injectors and/or the canister may need to be reduced and/or regulated to achieve such a purification efficiency as described. Moreover, delay (i.e., in time) in the arrival of the fuel vapor from the canisters to the internal combustion engine after starting the purge control may influence exhaust gas purification efficiency.
Also, recent developments in the automotive sector have shown that manufacturers are beginning to integrate forced induction and/or other artificial, non-naturally aspirated power enhancement devices to conventional internal combustion engines. Such devices may include supercharges, compressors, turbochargers (i.e., “turbos”) and/or any combination of the same. For example, in the case of the internal combustion engine configured with a supercharger, the pressure within the intake pipe may vary between negative and positive (i.e. relative to the outside atmospheric pressure) according to a pre-set supercharger condition and/or setting. Further, interruptions in airflow throughout the intake and/or exhaust system of a vehicle may occur due to backfires, for example, and may produce unwanted pressure variances and/or differentials in a vehicle intake pipe (i.e., an air intake pipe to provide fresh air to the internal combustion engine), even without a supercharger and/or turbocharger etc. For example, should the pressure within the intake pipe be negative (i.e., relative to the outside atmosphere), the fuel vapor within the canister may be drawn (i.e., suctioned) into the internal combustion engine via the intake pipe while the atmospheric air is introduced into the canister. In contrast, should the pressure within the intake pipe be positive, the fuel vapor within the canister may not be drawn into the internal combustion engine, as may be desirable for engine operation. Instead, the intake air may flow into the canister. Therefore, positive pressure within the intake pipe is most often not preferable for the purge control. For this reason, a check valve may be disposed in and/or on a purge passage connecting the canister and the intake pipe to permit and/or regulate flow of fluid in a direction from, for example, a side of the canister to a side of the intake pipe and also may prevent flow of the fluid in the opposite direction to that described. In such a case, a purge valve controlled by a controller may be disposed in and/or on the purge passage at a position on a side of the canister, and the check valve may be disposed in and/or on the purge passage at a position on a side of the intake pipe.
For example, Japanese Laid-Open Patent Publication No. 2006-57596 discloses a fuel vapor supply system with a purge valve disposed in and/or on a purge passage connecting a canister to an intake pipe at a position on a side of the canister. In detail, a check valve is disposed in and/or on the purge passage at a position on a side of the intake pipe. The fuel vapor supply system disclosed in Japanese Laid-Open Patent Publication No. 2006-57596 is generally configured such that vaporized fuel stored in the canister is supplied to the engine to improve cold start performance of the engine. Further, since the check valve, as described herein, is disposed in the purge passage, potential damage caused by, for example, a backfire may be avoided.
Also, Japanese Laid-Open Patent Publication No. 2007-198353 generally discloses a fuel vapor supply system for an engine with a supercharger. In detail, a purge valve is disposed in and/or on a purge passage connecting a canister and an intake pipe at a position on a side of the canister, and a check valve is disposed in and/or on the purge passage at a position on a side of the intake pipe. In the system disclosed by Japanese Laid-Open Patent Publication No. 2007-198353, the purge valve is opened at a predetermined time after stopping of the engine to, for example, avoid creating a residual negative pressure, i.e., a lower pressure in comparison to atmospheric pressure, within a part of the purge passage extending between the purge valve and the check valve. Accordingly, operational difficulties associated with such a residual negative pressure within the purge passage may be avoided.
Further, as initially described in Japanese Laid-Open Patent Publication No. 2007-198353, should the purge valve be disposed in and/or on the purge passage on a side of the canister, while the check valve is disposed in and/or on the purge passage on a side of the intake pipe, negative pressure may remain within part of the purge passage that extends between the purge valve and the check valve hereinafter referred to as the “intermediate purge passage.” On the condition that the purge valve is fully closed, the check valve may be opened if the pressure within the intake pipe is lower than the pressure within the intermediate purge passage. Thus, the pressure within the intermediate purge passage and the pressure within the intake pipe may equal each other. Alternatively, the check valve may be closed if the pressure within the intake pipe is not lower than the pressure within the intermediate purge passage. As a result, the pressure within the intermediate passage may be uniformly maintained.
Negative pressure, i.e. residual negative pressure, relative to atmospheric conditions, may be noticed both during vehicle (and engine) operation as well at rest (i.e. complete engine deactivation). For instance, should negative pressure, as described here and above, remain in the intermediate purge passage, purge control may be performed to open the purge valve. However, the check valve may remain closed, i.e. may not be opened, until the pressure within the intermediate purge passage increases to exceed the pressure within the intake pipe by air introduced into the canister. In detail, negative pressure within the intake pipe may cause the fuel vapor to be drawn into the canister after the check valve is opened. Thus, there may be a delay until the check valve is opened after the purge valve is opened. Such a delay may cause an increase in the time (i.e. delay time) necessary for the fuel vapor to arrive at the internal combustion engine after leaving the canister. As a result, if the fuel injection quantity of the injectors is reduced without adequately considering the increase of the delay time due to the aforementioned time lag, the reduction in the fuel injection quantity of the injectors may take place sometime before the arrival of the fuel vapor at the internal combustion engine. Thus, the quantity of the fuel may be insufficient relative to the quantity of the intake air, resulting an unfavorable lean condition (i.e., an air excessive condition) in comparison with the theoretical air-fuel ratio condition.
In view of that presented and discussed above, there is a need in the art for a technique of obtaining a pressure value within a part of a purge passage extending between a purge valve and a check valve for use in a purge control, without increase of the number of components of a fuel vapor supply system.